Amplifier circuit



June 17, 1930. L. M. HULL AMPLIFIER CIRCUIT Original Filed Nov. 1'7, 1926 amen 6oz Patented June 17, 1930 LEwIs vr. HULL, or MonnrAiN LAKES, NEW JERSEY, Assielvon 'ro RADIOFREQULNCY I LABORATORIES, noourone'rnn, or eoon'ron, new JERSEY,A CORPORATION or NE JERSEY AMPLiFIER CIRCUIT a original muse-tn filed November 17, 192 Serial 110,148,975. me jnt'm. ea e151, dated May 1, 1928.

Divided. and this application filed Marchi131928l application is a division of my copendin application Serial N 0. 148,975, filed November 17,1926. 9 o

' Thi's invention relates to an electrical am plifier circuit for use in associationwith a four-electrode vacuum tube of the-type having an emitting cathode, ananode, and two grid electrodes. For many purposes 'it-is desirable to operate such a vacuum tube ac-" o cording toa method, known inthisart, which includes employing the grid G which is'next thezcathode, or which-'istlie inner grid inra concentric; arrangement; asfthe control ele- Inent, andgivingto the grid-G whichls next 1 the anode, a positive bias.

'1 This method of: operating a four-electrode tube makes use of what may, for convenien'c'e,

be=termed the emission-shield eiiect of the rid G The result is an increase in the ef-V ectiv'e, alternatingcurrent plate impedance of, the tube, due tothe 'fact that the'efl'ectof the plate voltage upon the total electric field attracting the space current to the plate isgreatly reducedzbythe shielding action of the gridGg. Another effect is the reductionof the'elfective inter-electrode tubecapacity between the control grid, G and the plate, 7 and aconsequent reductionof undesirable retroactivecurrents which arefed back fromv plained,-' to the voltageiof control. grid G1, I can reduce to any 'desire 1extent,or supthe output circuit to the input ,circuit,

through these tube capacities. 1

, This etlnod of operating a lfour-electrode reducing or, suppressing these undesirable feedback currents in a four-electrode" vacuum tube when operated f an electrical an iplij' 11 have f und th by mp s' i e p the" rid,;G a voltage havingthe proper ampll-f e i [.pling coefiicientjbetween these coils are suittudeja'nd'phase relation, as willbe later e3} vacuum tube as an electrical amplifier does] Serial no. 261,292.

Press n si a f edk" omens:

which otherwise fiow' through' t he tube capacities o 1 i Th s may beacomplished in various ways,

certain typical ones of which I.- will now de-' scribe n connection the accompanying drawings.

Figures '1, 2,; 3,: and' l are diagrams illu's certain specific embodiments of my invention.

"Figured shows a four-electrode vacuum tube having emitting-cathode F, anodefQP,

(control) grid G a second (emission-shield) %rid G and'in'putf and output'circ uits 1 L1, and C2L2, espectively, The! 1111,6

putand output'circui'ts may be tuned or not as desired. They are here' shown as he-- a udions are cascaded or not.QTl1eA B77, and C batteries are arrangedas usual. The grid, G is [connected to the filament through coil L whi cl'1 is coupled to coil L in the input circuit, The properlypositive biasis' lmparted to the grid otherwise; j v. k In thi'sj 'cas'e coiljL' shouldfbe so wound with"respectfto'L c'thatj the compensating voltage mpressed upon} Ggl is" opposite in phase to the v'oltagetonthe grid G The amplitude of the "compensating voltage may beladjusted to give the desired suppression ofthe' feed-back currents. This may be done by giving L and L the proper coupling or in other ways. ;.Various,values of thercouable Ihaveused a" coeificient ofcoupling equal to ".5- with satisfactory results. The

H "G b'y including more T or less of the B battery in 16mm;

indicate that this capacity may be employed or omitted, as desired. hen employed, the capacity of C may, of course, be suitably adjustable.

An arrangement like that shown in Fig. 1 produces other beneficial results in addition to the suppression of feed-back currents. An important advantage arises from the secondary control efiect exerted by the grid G in Virtue of the coupling between coils L and L This control eflectmaybeof such ana ture that more constant amplification is obtained over a range of wavelengths.

In Figure 2 the compensating voltage is applied to the grid G by means of coil L coupled to coil L ofthe output circuit. The coil L should be so woundwith respect to-L that the voltage upon G is in phasewit-h the voltage upon G at vresonance; that, is, the

voltage upon Gr is'opposite' in phase tothe Y voltage upon the anode, P. The remainder of the circuitmay as before. e

In this arrangement, in addition to the suppression of feed-back currents, the-secappropriately be arranged V ondary control effect of grid G5 tends to in crease the amplification of the vacuum tube, Figure 3 shows an arrangement for applying the compensating voltage to the grid.

G by -means of coil L in series with coilL of the input circuit, but not necessarily coupled thereto. An isolating condenser C is then employed, and the tuning condenser C may be connected across both coils L and L as shown.

Figure & has already been referred to in describing Fig; 1. It shows one suitable method of cascading a plurality of"vacuum tube amplifiers arranged according to thisinvention. The circuit of Figurel is here il lustrated in cascade by wayof example only. The circuits as shown in the other figures may also be cascaded;

The circuits herein shown are ofcourse merely typical of the means which Iflhave found by experiment to be appropriate for carrying out my invention, by impressing the groper compensating voltage upon the grid Equivalent circuits for accomplishing this result, or variations of the circuits shown,

fall within my invent-ion.

I claim:

1. An electrical amplifier circuitcomprising an electron tube device having an emit ting cathode, an anode, a control grid, and

a second grid, said grids being positioned in the field between said anode and cathode; an output circuit associated with said cathode and anode; and an input circuit including inductance having one terminal connected to said control grid, an intermediate point connected to said cathode, and a second terminal connectedto said second grid.

2. An electrical amplifier c1rcu1t comprising an electron tube device having anemitting cathode, an anode, acontrol grid, and a secondgrid, said-grids being positioned in the field between said anode and cathode; an output circuit associated with-said cathode andanode; and-an input circuit includinginductance having one terminal connected to said control grid, an intermediate point connected to said cathode and a second terminal connected to saidsecond grid, and a tuning condenser connected: across said inductance.

3. An electron'tubedevice.having an emitting cathode, an anode, atcontrol grid, and

, a second grid, said grids beingpositioned in the field between saiduanode and cathode; an output circuit. associated with said cathode and anode; and an input circuit. includingfa coil-connected between said control. grid and saidcathode, and a secondcoil connectedin seriestherewith:between said cathode andsaidsecond, grid and wound. substantiallycontinuously with said first coil .4. ,Anelectron tube device having an emit.- ting cathode, an anode, acontrol grid, anda a.second grid; an output circuit associated with said cathode and anode; and an input circuitv including a 'coil connected between said controligrid'and said cathode, and a second coil connected-in series therewith between said cathode and saidsecond grid but. substantially uncoupled to said first coil.

5. An electron tube device. having an emitting cathode, an anode, a control grid, and asecond grid, said grids being positioned-in I the field between said anode and cathode; an

output circuit associated with saidicathodeand anode; and an input circuit including acoil connected between said control grid and said'cathode, anda second coil'connected in series therewith between said' cathode and said second grid, the winding'of said coilsforming a substantiallycontinuous inductive path between saidcontrol grid and said'sec- 0nd grid. 7 i V 6. An electron tube device'having'an emitting cathode, an'anode, a control grid, and" a second grid;'an' output circuit-associated with said cathode and'anode and an input circuit including a coil connected between said control gridand said cathode, and a sec-. ond coil connected in series therewith between said cathode andsaid second grid, the winding of said coils forming a substantially continuous inductive path between said'control grid andsaid second grid but said coils;

' being conductively by. an isolating condenser. V

7. An electron tube device having an emitting cathode, an anode, a control'g'rid, and a second grid, said grids being positioned in the field between said anode and cathode; an output circuit associated with said cathode and anode; and an input circuit 'in- V eluding a coil connected between said control grid and said cathode, a secondcoil connected inseries therewith between said cathode and said second grid and wound substantially continuously with said first coil, and a tuning condenser connected across-said coils.

In testimony whereof, I affix my signature.

LEWIS M. HULL.

separated from each other 7 

